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Date:   Tue, 19 Sep 2023 15:21:39 +0100
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Subject: Re: Arches that don't support PREEMPT
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To:     Peter Zijlstra <peterz@infradead.org>,
        John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc:     Matthew Wilcox <willy@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
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From:   Anton Ivanov <anton.ivanov@cambridgegreys.com>
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On 19/09/2023 14:42, Peter Zijlstra wrote:
> On Tue, Sep 19, 2023 at 03:37:24PM +0200, John Paul Adrian Glaubitz wrote:
>> On Tue, 2023-09-19 at 14:00 +0100, Matthew Wilcox wrote:
>>> On Tue, Sep 19, 2023 at 02:30:59PM +0200, Thomas Gleixner wrote:
>>>> Though it just occured to me that there are dragons lurking:
>>>>
>>>> arch/alpha/Kconfig:     select ARCH_NO_PREEMPT
>>>> arch/hexagon/Kconfig:   select ARCH_NO_PREEMPT
>>>> arch/m68k/Kconfig:      select ARCH_NO_PREEMPT if !COLDFIRE
>>>> arch/um/Kconfig:        select ARCH_NO_PREEMPT
>>>
>>> Sounds like three-and-a-half architectures which could be queued up for
>>> removal right behind ia64 ...
>>
>> The agreement to kill off ia64 wasn't an invitation to kill off other stuff
>> that people are still working on! Can we please not do this?
> 
> If you're working on one of them, then surely it's a simple matter of
> working on adding CONFIG_PREEMPT support :-)

In the case of UML adding preempt will be quite difficult. I looked at this a few years back.

At the same time it is used for kernel test and other stuff. It is not exactly abandonware on a CPU found in archaeological artifacts of past civilizations like ia64.

> 
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Anton R. Ivanov
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